The amplification of pressure and/or motion through the use of hydraulic cylinders and pistons is known. In such systems, a pair of hydraulic cylinders are connected in fluid flow relation and pistons are chosen having differing piston surface areas, with the relative amount of motions of the pistons being inversely proportional to their areas, so that an equal volume of space is displaced by each piston.
In the past, such systems were one-way systems. By this, it is meant that hydraulic fluid was positioned only on one side of the pistons. Spring, pneumatic or other pressure was required to reverse the stroke of such systems.
It was found that consistently accurate motion of such systems was difficult. Small amounts of hydraulic fluid loss, such as losses between the pistons and cylinder walls during reversing strokes, lead to decreases in the amount of hydraulic fluid between the pistons, thus adversely affecting the precise location for the initial and final positionings of the two pistons. When hydraulic motion being amplified by such a system was employed for movement of external parts connected to one of the pistons, such changes in the initial and final stroke positions could cause inaccurate positioning of the mechanical parts linked to this piston, thus leading to possible improper placement of these parts.
A further problem exists in the employment of such one-way hydraulic systems. Due to the lack of any constraining force on the piston being advanced by the hydraulic fluid, its velocity is not retarded, even when the velocity of the driving piston and the hydraulic fluid is reduced. Thus, vacuum or air pockets can form in the hydraulic line and accurate control of the velocity of the hydraulically moved piston is not possible. Vacuum pockets in the hydraulic line produce the phenomenom known as cavitation.